Description of problem:
=======================
squid-3.4.7-2.fc21.i686 crashes with "illegal instruction" and dumps core on an AMD Athlon(tm) XP 2400+

Yet the same package works correctly within a 32bit vm on an "AMD Athlon(tm) II X2 250" and also works on the same CPU where it crashed before, once simply recompiled and reinstaller with a quick:
$ mock squid-3.4.7-2.fc21.src.rpm
# yum reinstall ./squid-3.4.7-2.fc21.src.rpm

=== Log extract (reversed) ===
Dec 18 17:23:36 lanserve.idp.it systemd[1]: squid.service failed.
Dec 18 17:23:36 lanserve.idp.it systemd[1]: Unit squid.service entered failed state.
Dec 18 17:23:36 lanserve.idp.it systemd[1]: Failed to start Squid caching proxy.
Dec 18 17:23:36 lanserve.idp.it systemd[1]: squid.service: control process exited, code=exited status=132
Dec 18 17:23:36 lanserve.idp.it cache_swap.sh[274]: init_cache_dir /var/spool/squid... /usr/libexec/squid/cache_swap.sh: line 11:   279 Illegal instruction
   (core dumped) squid -N -z -F -f $SQUID_CONF >> /var/log/squid/squid.out 2>&1
Dec 18 17:23:36 lanserve.idp.it named[270]: running
Dec 18 17:23:36 lanserve.idp.it systemd[1]: Starting Squid caching proxy...

=== Additional Info ===
cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 8
model name      : AMD Athlon(tm) XP 2400+
stepping        : 1
cpu MHz         : 2015.118
cache size      : 256 KB
physical id     : 0
siblings        : 1
core id         : 0
cpu cores       : 1
apicid          : 0
initial apicid  : 0
fdiv_bug        : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse syscall mmxext 3dnowext 3dnow vmmcall
bugs            : fxsave_leak
bogomips        : 4030.23
clflush size    : 32
cache_alignment : 32
address sizes   : 34 bits physical, 32 bits virtual
power management: ts